Effects of postharvest ethanol vapor treatment on the ascorbate-glutathione cycle in broccoli florets

Broccoli (Brassica oleracea L Italica Group) senesces very rapidly at room temperature after harvest. Ethanol vapor treatment suppresses the senescence. Reactive oxygen species (ROS) are closely related with postharvest quality of horticultural crops, and the ascorbate-glutathione cycle plays a crucial role in controlling the level of ROS. The effects of postharvest ethanol vapor treatment on the cycle in broccoli florets were investigated to clarify the inhibition of senescence with ethanol. Broccoli branchlets were packed in a perforated polyethylene bag with or without a 3 g ethanol pad and stored at 20 degrees C in darkness. The ethanol concentrations in the atmosphere of the bag containing the ethanol pad were about 40 pmol mL(-1). In control and ethanol-treated broccoli, the contents of L-ascorbic acid and reduced glutathione decreased during storage, but the decrease in control broccoli was more marked than that in ethanol-treated broccoli. The ascorbate peroxidase activities in ethanol-treated broccoli were constant during storage, whereas the activities in the control broccoli decreased almost linearly. The glutathione reductase activities in ethanol-treated broccoli were higher than those in the control at 5 d in storage (DIS). The dehydroascorbate reductase activities in ethanol-treated broccoli decreased gradually. On the other hand, the activities in the control broccoli decreased gradually until 3 DIS and then considerably. These results suggest that ethanol vapor treatment might suppress the decrease in reducing substances and enzyme activities associated with the ascorbate-glutathione cycle to reduce oxidative stress through effective removal of hydrogen peroxide, and the suppression might partly contribute to the suppression of senescence in ethanol vapor-treated broccoli. (C) 2008 Elsevier B.V. All rights reserved.